Ammonia recovery



Nov. 1'?, 1931. c, c. HERITAGE ET AL 1,832,485

AMMONIA RECOVERY v Filed Maron 27, 1925 NOV 17, 1931- c:A c. HERITAGE ET AL 1,832,485

AMMONIA RECOVERY Filed March 27, 192e 2 sheets-sneer 2 Patented Nov. 17, 193i asians UNETED lSTATES PATENT OFFICE` CLARK C. HERITAGE AND IRVING T`. THORNTON, OF BUFFALO, NEW YORK, ASSIGNORS TO NATIONAL ANILINE & CHEMICAL CO., INC., OF NEW YORK, N. Y., A CORPORATION OF NEW YORK AMMONIA RECOVERY Application med March 27, 192e. serial No. 97,983.

monia, remaining in the reaction vessel after completion oi' the reaction, be recovered and reused. The recovery of the ammonia is `effected, according to common practice, by

3assin r the ortion of the reaction mixture which is in the vapor phase intoV an absorption tower containing water. rlhe ammonia 37 is absorbed by the water, but owing'tothe varying content oi' steam 'and ammonia in the reaction mixture and the variation in the pressure and temperature conditions asgthe pressure in the autoclave falls, the' absorption l is irregular and the concentrationofthe re- Y sultinq ammonia liquor cannot becontrolled. It is desirable. however, when employing unskilled labor for recharging the autoclave for subsequent operation, that there always be used an aqueous ammonia of a particular strength; and so, in practice, the aqueous solution obtained by absorption is distilled and rectified. :recording to the' present.A invention, Ava

the escaping gases.

vbottom ofa solution tank or absorber l2.

process and apparatus are provided whereby In the practice of the present invention for the recovery of gaseous products contained in a` reaction mixture under superatmosplieric pressure, the pressure of that portion of the reaction mixture which is in the vapor phase is reduced, the portion is then cooled to produce a condensate, the uncondensed residue is separated from the condensate, and gaseous products are absorbed from said uncondensed residue in a liquid medium, while maintaining said,

medium under iixed temperature and pressure conditions. f In the accompanying drawings Fig.` l lshowsdiagrammatically an apparatus for carrying out the process of the invention; and

Fig. 2 is a section oi a solution tank.

vAn autoclave 1 has a vapor line 2 extending from it with needle valves 3, 4 and associated pressure gages 5, 6 to regulate the pressure of The vapor line 3 is connected to acooling coil or condenser 7 and this in turn opens into a separating tank 8 below a normal liquid level maintained therein. p

A pipe line l0, provided with a needle valve 1l, leads from tank 8, at a point above the normal liquid level in said tank, to the A pipe line l0 leads from the first absorber to a second solution tank or absorber 13, which is connected by a line 42 to the bottom of a tower 14 having a vent l5 to the atmosphere. The solution tanks or absorbers l2 and 13, and the tower 14 contain water or other liquid.`

Each of the tanks l2 and i3 and the tower 14 have valve controlled bottom outlets, 16,

17, 18 19, respectively, connected to a common main 20, which is inclined so as to drain into containers or storage tank 2l and 22. Theyfalso have valve controlled top inlets, 23. 24, 25, 26, respectively, connected to a common water or liquid header 27. rlhe second solution tank 13 is at a higher'level CIK v7 o ipc,

than the first, so that it may be emptied into the latter, While the toiver 14 is preferably at about the same level with the second solution tank. rl'he tanks are equipped With gage glasses 2S, 29, 30, respectively. The separation tank and the first solution tank 12 have pressure gages 31, 32 and are further provided with samplers 38, 34. The separator and absorbers are also each provided with a safety valve.

rJ'he first absorber or solution tank 12 is shown in section in Fig'. 2. TNithin the tank there a double cooling' coil Around the bottom there is a partial turn 3G of a large diameter pipe into or near one end of which there extends the terminal 37 of the gas admission line 10 thus forming an injector. Pertorations 38 near the outlet end 39 cause a ditl'usion ot the gases and entrained liquid throughout the mass ot liquid Within the tank. A thermometer 40 is inserted in the tank to indicate temperatures.

In carrying out the process ot the inven tion in connection with the apparatus described, a mixture ot vapor and rases is con* tained under high pressure in the pressure vessel 1. Needle valves 3 and i are then opened, permittingr a stream ot the mixture to flow into the condenser 7. T he expansion of the mixture in its passage through the needle valves trom the high pressure in the container to the lower, though still elevated, pressure in the condenser results in a decided cooling of the mixture. This cooling, assist- 'f ed by the cooling action of the condenser and the pressure retained on the mixture, results in the ready liquefaction of the condensible vapors, such steam, in the passage of the mixture through the condenser. The cooled mixture, containing` the condensate, t-hen passes into separator 8 Where the condensate is trapped, and the dried or separated gases tloW through line 10 and needle valve 11 into the solution tank or absorber 12, which is 's partially filled with absorbing` liquid.

uid in the solution tank 12, the injector ac coil tif

In iiassing through the needle valve 11, the gases e further expanded to a lower, though still elevated, pressure and cooled. The l`eases are absorbed in the absorbing' liqtion produced by the ,frases in entering' the tank 12 resulting` in thorough intermixture of the gas and absorbing' liquid. Heat liberated by the absorption is removed by the cooling Unabsorbed l`frases then pass through line 10 into the second absorber 13, Where an additional portion of the gases is absorbed. The second absorber 13 is preferably partially ,tilled with an absorbing liquid similar to that in tank 12, the extent to which it is filled being' dependent upon the pressure desired to be maintained on the exit gases in the first absorber 12. Residual gases are scrubbed in tower 14.

This process affords a means et directly obtaining a solution of the gas in the absorbing,r liquid having a particular concentration of dissolved gas. By removing' condensible material as a separate stage of the process and then absorbing the gas Which has been freed from eondensible material, it becomes possible to control the concentration ot the absorbed gas in the solution by a mere control ot the temperature and pressure conditions in the solution tank, inasmuch as a liquid n'ill absorb only a. xed amount of a particular gas under {ixed conditions of partial pressure of the gas and temperature.

The Jfollowing' specitic example. illustrative of the process and the apparatus ot thc present invention, describes their usc in connection with the manufacture ot betaminoanthraquinone.

Example: The autoclave is charged with aqua ammonia ot about 28% strength to which is added copper sulfate and chlor-anthraquinone. It is then closed and heated to about 200 C. and maintained at this temperature for the necessary reaction period; the pressure rises to about 800 or 850 poundsA per square inch. At the end ot the reaction the gaseous constituents of the reaction mixture are gradually released by means ot thc needle valves 3, Ll and allowed to expand to a. pressure ot about 50 pounds per square inch. The expansion causes a considerable drop in temperature, and heat is eliminated as thc gaseous products flow through the cooling; coil 7 resulting in a concentrated ammonia condensate. The condensate remains substantially in the separator S. The dried or separated gases pass trom the separator 8 to the first solution tank or absorber 1 2. and are further expanded to a pressure of about 5 pounds per square inch in their passage through the needle valve 11, thus beiner turther cooled. Sutiicient pressure is maintained on the gases to give a desired velocity and an injector action in the tirst solution tank or absorber 12 which is preterably charged with a measured quantity of Water. later is dra wn Yby the injector through the pipe 2% in contact With the ammonia in the gases` and the ammonia-water mixture is diffused into thrbalance of the water. rl`he ammonia absorption releases heat which is removed by the cooling' coil 35, a sutlicient amount ot coolingl medium being circulated through the coil to maintain a.' desired temperature comnieirsu` rate with the concentration ot aqua ammonia` that is desired; thus a temperature of 2550 t". or thereabouts With a proper charge of Water and a pressure on the entering' ammonia ot about 5- pounds per square inch rives an aqua ammonia ot about 28% concentration. linabsorbed gases pass through line 10 into thil second solution tank or absorber l?) which is nominally at atmospheric pressure; and wird' escapes from this tank passes through the liquid in the tower 14 and out ofv the vent ttl 15.y 'The second solution tank has acharge of water preferably equal .to that inthe tiret Vso that the latter can be filled `trom. tle

' the vapor phase, and the proportion ot steam in the Gases increases while the )roeortion ot ammonia decreases. This is indicated by 'the' rising` level of water in the separation tank and the decreased flow of ammonia into the first absorber; but as the condensate is trapped in the separation tank, it does not di- .lute the aqua ammonia formed in the absorber. Consequently, the absorber can be charged with a definite amount of water corresponding to the amount of ammonia given oli during the reaction,v and an aqueous ammoniay solution of the desired strength can be obtained in the solution tank by regulating the temperature and pressure conditions to correspond with equilibrium conditions of aqueous ammonia of said strength.

Vhen the recovery ot ammonia is tinished, the tanks may be sampled and concentrated liquor from the separation tank .and solution from the absorber allowed to escape in proportions to givethe desired strength to be collected in the containers 2l, 22. ,Vhen this has been accomplished the valves to the containers are closed, the outlet to the separation tank is closed and the second solution tank is drained into the iirst. The first solution tank outlet is then closed and the second solution tank is illed from the tower and supplied with any necessary additional water. rlhereupon the bottom outlets to the second solution tank and tower are closed and the apparatus is ready for a second run, following the discharge of the autoclave and recharging ot' the latter. Prior to preparing the tanks for a second run, any excess in the tanks can be drained into the sewer line 4,1; The aqua ammonia thus collected in the containers 2l, 22 is ready for use in the autoclave reaction without any further treatment.

The expansion of the gaseous produc-ts through the needle valves 'tromtlie high prossures in the autoclave results in a decided cooling of these products so that condensible vapors, such as steam,'readilv become liquid in traveling through the condenser. This liquefaction is further accelerated by the pressure retained on the gases. The pressure'also results in an increased absorption of ammonia by the condensate, giving an aqua ammonia of high concentra-tion. Accordingly in the condensation step no liquid is added, and heat .7 `Fur-ther cooling follows from the expansion into the rst absorberor solution tank. A high velocity of the gases also results, and lin passing-through the injector, the liquid in the absorber is drawn in, and intimate contact of gas and liquid is obtained. The liquid and absorbed gases rise to the top and in so doing pass over the cooling coils which remove the heat of absorption.

`While the gas expansions are secured by Vreductions ot a high initial pressure, other 4pressures or a partial vacuum on the end of the system can be used 'for this purpose. `Furthermore the degree to which such expansions occur depends on the relative pressures, and lthese can be controlled or varied in accordance with the products desired.

Though the invention is primarily directed to ammonia recovery, its application to the recovery of other products of a similar nature is evident. Consequently it is not to be interpreted as restricted to the specific example given but is to be `given a scope commensurate with the appended claims.

What is claimed is:

l. The process of recovering gaseous and liquid products from a chemical reactionv mixture',which comprises reducing the pressure of that portion of the reaction mixture which I is in the vapor phase, cooling said portion to l produce a condensa-te, separating the un- -condensed residue from the condensate, further reducing the pressure of the uncon- Fdensed residue and absorbing products from said uncondensed residue in a liquid medium, until a predetermined ixed pressure to which kthe liquid medium is subjected is reached, whereby a solution of lixed concentration is y `termed.

2; The process of recovering gaseous and liquid products from a chemical reaction mix- -ture containing` the same under superatmospheric pressure, which comprises reducing the Vpressure of that portion of the reaction mixture which is in the vapor phase,`cooling said portion to produce a condensate, separating the uncon densed residue from the condensate, "further reducing the pressure of said uncondens'ed residue, andabsorbing gaseous productsY therefrom in a liquid medium, while maintaining said medium under temperature and pressure conditions corresponding with equilibrium conditions of a solution of fixed concentration of said gas in said medium.

The process of recovering ammonia from a reaction mixture which contains ammonia `gas and water vapor, which comprises reducing the pressure of that portion of the reaction mixture which is in the vapor phase, cooling portion to condense water vapor, separating the uncondensed residue from the condensate, further reducing the pressure of the uncondensed residue and passing said residueA into anaqueous absorbing` medium, until a predetermined fixed pressure to which Cil Llil

the liquid medium is subjected is reached, wherebyY a solution of fixed concentration is formed.

4,-. The process of recovering ammonia from a reaction mixture which contains ammonia gas and Water vapor under superatmospheric pressure, which comprises expanding that portion ot the reaction mixture including ammonia and water vapor which is in the vapor phase, cooling said portion to condense substantially all Water vapor con tained therein, separating the uncondensed `esidue from the condensate, including ammonia ,gas anl passing said residue including tbe ammonia into an aqueous absorbing medium, until a predetermined fixed pressure to which the liquid medium is subjected is reaclied to form an ammonia solution of xed concentration.

5. A process which comprises chemically reacting reagents includin aqueous ammonia ot a xed concentration to t'orm a reaction mixture under superatmosplieric pressure and comprising gaseous products including ammonia, reducing tlie pressure of said gaseous products, cooling said products to torm a condensate, separating the condensate trom the uncondensed residue, absorbing airmonia from said uncondensed residue in an aqueous medium while maintaining said Inediuin under temperature and pressure conditions corresponding With the equilibrium conditions ot an aqueous ammonia of substantially the concentration originally employed` and repeating the reaction with said ammonia as a reagent.

6. A process which comprises chemically reacting reagents including an aqueous ammonia solution ot about 28 per cent. strength to torni a reaction mixture under a pressure greater than about 50 lbs. per square inch and comprising gaseous products including ammonia and Water vapor. reducing the pressure ot' said gaseous products to about 50 lbs. per square inch. cooling said products to condense water vapor, separating residual uncfmdensed products from the condensate, reducing the pressure ot said uncondensed products to about 5 lbs. per square inch, absorbing` ammonia, trom said uncondensed products in an aqueous medium, While maintaining said medium at a temperature of about 35 C. and at a pressure of about 5 lbs. er square inch to produce an aqueous anunonia solution ot' about 28 per cent. strength, and repeating` the reaction with said ammonia as a reagent.

Apparatus for recovering gaseous products ot a reaction, comprising in combination means -l'or reducing the pressure of aV gaseous mixture, said means being adapted to be connected to a reaction vessel, a condenser connected to said means, means for trapping condensate connected to said condenser, and absorbing means connected to said latter means.

S. Apparatus for recovering gaseous products of a reaction, comprising in combination means for reducing the pressure ot a gaseous mixture, said means being adapted to be connected to a reaction vessel, a condenser connccted to said means, means for trapping condensate connected to said condenser, pressure reducing means connected to said trapping means, and absorbing means connected to said latter pressure reducing means.

9. Apparatus for recovering gaseous products of a reaction, comprising in combination a pressure reducing valve, said valve being adapted to be connected to a reaction vessel, a condenser connected to said valve, a trap for condensat-e connected to said condenser, pressure reducing means connected to said trap, an absorber connected to said means, and a cooler tor said absorber.

l0. Apparatus for producing aqua ammonia ot a definite concentration from a gaseous mixture containing ammonia under pressure, comprising in combination means for expanding said mixture, said means being adapted to be connected to the container ot said mixture, means for condensing vapors contained in said expanded mixture, means tor removing condensed vapors from said cxpanded mixture, means for absorbing ammonia from said expanded mixture, and means for controlling the temperature and pressure in said absorber.

ll. Apparatus for producing aqua ammonia of a definite concentration trom a gaseous mixture containing ammonia under pressure, comprising in combination means for expanding said mixture, said means being adapted to be connected to the container of said mixture, means for condensing vapors contained in said expanded mixture, means for removing condensed vapors from said expanded mixture, means for further expanding the residual gases, means tor absorbing ammonia from said gases, and means for controlling the temperature and pressure in said absorber.

l2. Apparatus for producing aqua animonia ot a definite concentration from a gaseous mixture containing ammonia under pressure, comprising in combination a pressure reducing valve, said valve being adapted to be connected to the container of the gaseous mixture, a condenser connected to said valve, a separator for removing liquid condensate connected to said condenser and having a gas outlet, an al sorbcr connected to said outlet, a cooler for said absorber, and means for regulating the pressure in said absorber.

18. Apparatus for producing aqua ammonia of a definite concentration from a gaseous mixture containing ammonia under pressure, comprising in combination a ressure reducing valve, said Valve being a apted to be connected to the Container of the gaseous mixture, a condenser connected to said Valve, a separator for removing liquid condensate connected to said condenser and having a gas outlet, an absorber, a pressure reducing .valve connecting said absorber to said outlet, a cooler for said absorber, and means for regulating the pressure in said absorber.

In testimony whereof We affix our signatures.

CLARK C. HERITAGE. IRVING T. THORNTON.

CERTIFICATE or CORRECTION, Patent No. 1,832,485. Granted November 17, 1931, to

CLARK o. HERITAGE ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, line 66, for the numeral "3" read 2; page 4, lines 13 and 14, claim 4, strike out the words "including ammonia gas" and insert including the ammonia gas to follow "residue" in line 13, of same claim; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 22nd day of December, A. D. 1931.

M. J. Moore, (Seal) Acting Commissioner of Patents. 

